1. Field of the Invention
Embodiments of the invention relate to a projection lens unit adapted for use in an exposure process, as well as an exposure apparatus including the projection lens unit and a control method adapted to focus and level the projection lens unit. More particularly, embodiments of the invention comprise a projection lens having adjustable properties used to focus and level the projection lens unit.
This application claims the benefit of Korean Patent Application No. 10-2004-0069873 filed on Sep. 2, 2004, the disclosure of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
Continued improvement of semiconductor device performance depends to a great degree on high levels of reliability, increased operating speed and greater integration densities. These demands require continuous improvement in the fabrication technologies used to manufacture semiconductor devices. The fabrication of semiconductor devices is accomplished by a complex sequence of individual processes. Many of these processes are used to form circuit patterns on the surface of a semiconductor substrate. The photolithography and similar fabrication processes used in the formation of circuit patterns often involve an exposure process in which the surface of the semiconductor substrate is selectively illuminated with light emitted from a light source. This process is generally referred to as “projecting.” Light is typically projected through a mask or a reticle in order to form a light pattern corresponding to all or part of a circuit pattern to be formed on the semiconductor substrate.
For example, in some exposure processes, a circuit pattern defined by the mask or reticle is transferred to a photosensitive layer (e.g., a photoresist layer) formed on the semiconductor substrate. In these type of exposure processes, it is very important to properly control the focal properties and irradiation angle (e.g., the level of the exposure beam) of the light being projected onto the photoresist layer.
Unfortunately, the mechanical vibrations associated with the rapid manufacture of semiconductors devices in a modern fabrication line make it quite difficult to maintain proper focus and level. In order to ensure the accurate transfer of circuit pattern information from a mask or reticle to a semiconductor substrate, it is first necessary to perform a focus control operation prior to projecting the irradiating light. The focus control operation ensures that the proper portion (i.e., the “shot area”) of the semiconductor substrate is irradiated by the exposure beam. After the focus control operation is complete a leveling control operation is performed to ensure a desired angular relationship is established between the semiconductor substrate and the exposure apparatus in relation to the shot area.
A schematic view of the conventional exposure apparatus adapted for use in a conventional exposure process is shown in FIG. 1. The conventional exposure apparatus incorporates a conventional level condition measurement unit includes a light source 10 adapted to generate an exposure beam, a reticle 20, a projection lens 30, a focus and level condition measurement unit (41 and 42), and a semiconductor substrate stage 60.
Within this conventional arrangement, light source 10 provides an exposure beam R10 intended to irradiate semiconductor substrate 50 through reticle 20. Projection lens 30 is adapted to miniaturize and transfer the circuit pattern defined by reticle 20 onto semiconductor substrate 50. Semiconductor substrate 50 is positioned on stage 60 under projection lens 30, and stage 60 is adapted to be moved in the X-, Y- and Z-directions to allow complete exposure of semiconductor substrate 50.
Prior to this exposure process, focus and level condition measurement process(es) must be performed. Unless the focus and level conditions are properly defined the circuit pattern will not be accurately transferred to the semiconductor substrate and the manufacturing yield for the semiconductor device will suffer accordingly. The focus and level condition measurement unit(s), including a light emitting device 41 and a light receiving device 42, generally measure the focus and level conditions associated with semiconductor substrate 50 in relation to projection lens 30.
Light emitting device 41 irradiates semiconductor substrate 50 with a reference light R20a. Light receiving device 42 detects a portion of reference light R20b reflected from semiconductor substrate 50. For example, the focus and level conditions of semiconductor substrate 50 are measured in relation to the reference light R20b reflected from four corners of a current shot area. Using measurement data derived from the reflected reference light R20b, semiconductor substrate stage 60 may be moved in the X-, Y- and Z-directions in order to obtain the desired focus and level conditions for semiconductor substrate 50 relative the current shot area.
As can be seen from the foregoing, the conventional focus and level condition measurement unit functions independent of projection lens 30. Thus, the measured focus and level conditions fail to account for variations (e.g., temperature, humidity, etc.) in the actual inner conditions of projection lens unit 30. Further, potential distortions or particular magnification effects associated with projection lens 30 are not accounted for in the conventional focus and level condition measurements. As a result, the circuit pattern transferred to semiconductor substrate 50 may be deformed despite the conventional efforts to control focus and level conditions.